2.3 Cellular componentsThe different leukocyte types derived from the lymphoid and myeloid lineages known from mammals have also been recognized in fish, including cells morphologically and functionally equivalent to mammalian B and T lymphocytes, natural killer (NK) cells, monocytes, macrophages, neutrophils, eosinophils, mast cells, and thrombocytes (Secombes, 1996; Whyte, 2007), as well as th..